OpenGL
(called GL in other pages) is a high-performance 3D-oriented renderer. It
is available in the X window system through the GLX extension. To determine
whether the GLX extension is supported by an X server, and if so, what
version is supported, call glXQueryExtension and glXQueryVersion.

GLX extended
servers make a subset of their visuals available for OpenGL rendering. Drawables
created with these visuals can also be rendered using the core X renderer
and with the renderer of any other X extension that is compatible with
all core X visuals.

GLX extends drawables with several buffers other than
the standard color buffer. These buffers include back and auxiliary color
buffers, a depth buffer, a stencil buffer, and a color accumulation buffer.
Some or all are included in each X visual that supports OpenGL.

To render
using OpenGL into an X drawable, you must first choose a visual that defines
the required OpenGL buffers. glXChooseVisual can be used to simplify selecting
a compatible visual. If more control of the selection process is required,
use XGetVisualInfo and glXGetConfig to select among all the available visuals.

Use the selected visual to create both a GLX context and an X drawable.
GLX contexts are created with glXCreateContext, and drawables are created
with either XCreateWindow or glXCreateGLXPixmap. Finally, bind the context
and the drawable together using glXMakeCurrent. This context/drawable pair
becomes the current context and current drawable, and it is used by all
OpenGL commands until glXMakeCurrent is called with different arguments.

Both core X and OpenGL commands can be used to operate on the current drawable.
The X and OpenGL command streams are not synchronized, however, except
at explicitly created boundaries generated by calling glXWaitGL, glXWaitX,
XSync, and glFlush.

Below is the minimum code required to create
an RGBA-format, X window that's compatible with OpenGL and to clear it to
yellow. The code is correct, but it does not include any error checking.
Return values dpy, vi, cx, cmap, and win should all be tested.

A color map must be created and passed to XCreateWindow. See the
preceding example code.

A GLX context must be created and attached to an
X drawable before OpenGL commands can be executed. OpenGL commands issued
while no context/drawable pair is current result in undefined behavior.

Exposure events indicate that all buffers associated with the specified
window may be damaged and should be repainted. Although certain buffers
of some visuals on some systems may never require repainting (the depth
buffer, for example), it is incorrect to write a program assuming that
these buffers will not be damaged.

GLX commands manipulate XVisualInfo structures
rather than pointers to visuals or visual IDs. XVisualInfo structures contain
visual, visualID, screen, and depth elements, as well as other X-specific
information.

All supported GLX extensions will have
a corresponding definition in glx.h and a token in the extension string
returned by glXQueryExtensionsString. For example, if the EXT_visual_info
extension is supported, then this token will be defined in glx.h and EXT_visual_info
will appear in the extension string returned by glXQueryExtensionsString.
The definitions in glx.h can be used at compile time to determine if procedure
calls corresponding to an extension exist in the library.

OpenGL itself
has also been extended. Refer to glIntro for more information.

GLX 1.2 is now supported. It is backward compatible with GLX 1.1 and
GLX 1.0.

GLX 1.2 corresponds to OpenGL version 1.1 and introduces the following
new call: glGetCurrentDisplay.

GLX 1.1 corresponds to OpenGL version 1.0 and
introduces the following new calls: glXQueryExtensionsString, glXQueryServerString,
and glXGetClientString.

Call glQueryVersion to determine at runtime what
version of GLX is available. glQueryVersion returns the version that is
supported on the connection. Thus if 1.2 is returned, both the client and
server support GLX 1.2. You can also check the GLX version at compile time:
GLX_VERSION_1_1 will be defined in glx.h if GLX 1.1 calls are supported and
GLX_VERSION_1_2 will be defined if GLX 1.2 calls are supported.